This invention relates generally to fuel injectors having check valves, and more particularly to fuel injectors having a direct hydraulic control of check valves.
Known hydraulically-actuated fuel injection systems and/or components are shown, for example, in U.S. Pat. Nos. 5,687,693 and 5,738,075 issued to Chen and Hafner et al. on Nov. 18, 1997 and Apr. 14, 1998, respectfully.
In these hydraulically actuated fuel injectors, a spring biased needle check opens to commence fuel injection when pressure is raised by an intensifier piston/plunger assembly to a valve opening pressure. The intensifier piston is acted upon by a relatively high-pressure hydraulic fluid, such as engine lubricating oil, when an actuator driven fluid control valve, for example a solenoid driven fluid control valve, admits high-pressure hydraulic fluid to act on the intensifier piston.
Injection is ended by operating the actuator to release pressure above the intensifier piston. This in turn causes a drop in fuel pressure causing the needle check to close under the action of its return spring and end injection.
Recently, Caterpillar Inc. has developed a new generation of fuel injectors, such as the HEUI-xe2x80x9cBxe2x80x9d(trademark) fuel system fuel injector, that feature direct control of the spring biased needle check valve. In these fuel injectors, even when fuel pressure has been raised by the intensifier piston to the valve opening pressure, the check valve can be kept shut (or quickly shut if it is open) by applying high-pressure hydraulic fluid directly to a check control chamber to create closing bias on the needle check valve.
A critical component of both types of hydraulically actuated fuel injector is the actuation fluid control valve, which admits the high-pressure hydraulic fluid to the injector. In hydraulically actuated fuel injectors with direct check control the actuation fluid control valve is especially critical because it must be able to control both the intensifier piston and the check valve.
For example, in a HEUI-B(trademark) fuel injector described in co-pending U.S. patent application No. 09/358,990 filed Jul. 22, 1999, claiming priority from U.S. provisional application No. 60/110,897 filed Dec. 4, 1998, and entitled xe2x80x9cHydraulically Actuated Fuel Injector with Seated Pin Actuatorxe2x80x9d a two-way valve is used both to apply direct control on the check valve, and also to operate a spool valve that controls actuation of an intensifier piston.
With that valve, when high-pressure hydraulic fluid is directed to apply closing bias on the check valve, the spool valve begins to move to drain pressure on the intensifier piston. Although the check valve closes immediately, full pressure is maintained on the intensifier piston for a while after the check valve is closed because of hysteresis in the spool valve. However, eventually hydraulic fluid pressing down on the intensifier piston begins to drain, reducing fuel pressure in the nozzle chamber.
When time separation between two fuel injection events or xe2x80x9cshotsxe2x80x9d is small, the spool valve hysteresis maintains pressure on the intensifier piston until the second shot is completed, so the second shot has good injection characteristics. But as shot separation increases, the time available for the spool to return and drain the pressure on the intensifier piston increases. Once the spool returns fuel pressure begins to decrease, and injection characteristics of the second shot become a function of the separation time.
For at least this reason, it would be advantageous in some applications to keep fuel pressure in the nozzle chamber high for a longer time. Unfortunately, current fuel injectors described above keep the fuel pressure high for only a fixed length of time after direct check control closure. It would be better if fuel pressure in the nozzle chamber could be kept high indefinitely, for a controllable length of time.
Ideally, a control valve would be capable of supplying hydraulic fluid to the intensifier piston and to the check control chamber independently, or otherwise achieve independent control of separate closing and opening biases on the check valve. No feasible method of accomplishing this has hitherto been found.
The present invention is directed to addressing one or more of the topics discussed above.
In a first aspect of the invention, a hydraulically actuated fuel injector comprises a nozzle, a check, a check control chamber, and an actuation valve member. The nozzle has a nozzle orifice and a nozzle chamber.
The check is movable between an open position that allows fluid communication between the nozzle chamber and the nozzle orifice, and a closed position that stops fluid communication between the nozzle chamber and the nozzle orifice. The check control chamber is disposed such that fluid pressure in the check control chamber will exert a closing bias on the check.
The actuation valve member is fluidly connected with a high-pressure supply line, a low-pressure drain line, a check control line fluidly connected with the check control chamber, and a pressure control line. The actuation valve member is positionable at first, second, and third positions.
The first position of the actuation valve member fluidly connects the pressure control line to a first line of the high-pressure supply line and the low-pressure drain line.
The second position of the actuation valve member is different from the first position, fluidly connects the check control line to the high-pressure supply line, and fluidly connects the pressure control line to a second line of the high-pressure supply line and the low-pressure drain line. The second line is different from the first line.
The third position of the actuation valve member is different from the first and second positions, fluidly connects the check control line with the low-pressure drain line, and fluidly connects the pressure control line to the second line.
In a second aspect of the invention, a method is disclosed for controlling a hydraulically actuated fuel injector having a check, an intensifier piston, a nozzle chamber, and an electronically controlled actuator attached with an actuation valve member positionable at at least first, second, and third positions.
The method comprises positioning the actuation valve member at the first position to drain high-pressure hydraulic fluid biasing the intensifier piston, thereby reducing fuel pressure in the nozzle chamber and allowing more fuel to enter the fuel injector; positioning the actuation valve member at the second position to cause high-pressure hydraulic fluid to increase hydraulic bias against the intensifier piston, thereby pressurizing fuel in the nozzle chamber to a first pressure and causing the pressurized fuel to be injected from the nozzle chamber at the first pressure; and positioning the actuation valve member at the third position to cause high-pressure hydraulic fluid to create a closing bias on the check to halt fuel injection while keeping fuel in the nozzle chamber pressurized to at least the first pressure until the actuation valve member is positioned at the second position.
In a third aspect of the invention, a method is disclosed for operating a fuel injector. The method comprises starting fuel injection by producing positive opening hydraulic bias on a check; stopping fuel injection by producing positive closing hydraulic bias on the check; and achieving independent control of production of both the positive opening hydraulic bias and the positive closing hydraulic bias by electronically controlled movement of a single actuation valve member.
In a fourth aspect of the invention, a method is disclosed for controlling a hydraulically actuated fuel injector comprising a check, a nozzle chamber, and an electronically controlled actuator attached with an actuation valve member. The method comprises positioning the actuation valve member at a first position to cause pressurization of fuel in the nozzle chamber to an injection pressure and injection of the fuel from the nozzle chamber at the injection pressure, and positioning the actuation valve member at a second position, different from the first position, to hydraulically bias the check to halt fuel injection from the nozzle chamber while keeping the fuel pressure in the nozzle chamber at the injection pressure indefinitely.
In a fifth aspect of the invention, a hydraulically actuated fuel injector comprises to pressurization means for pressurizing fuel in the fuel injector, check bias means for directly operating a check to stop fuel injection by applying hydraulic bias to the check, and control means for independent control of the pressurization means and the check bias means.